#include #if 1 && defined(LOCAL) #include #else #define debug(...) #define line #endif using namespace std; typedef long long ll; typedef long double ld; #define all(x) (x).begin(), (x).end() #define rall(x) (x).rbegin(), (x).rend() template inline bool chmax(T &a, T b) { return ((a < b) ? (a = b, true) : (false)); } template inline bool chmin(T &a, T b) { return ((a > b) ? (a = b, true) : (false)); } int main() { int N; cin>>N; cout<<((1+N)*(N))/2<